The hallmark of having gone through the Upanayana ceremony is the wearing of the Yajñopavitam (Sacred Thread) on the body. The thread is circular, being tied end-to-end (only one knot is permissible); it is normally supported on the left shoulder(savya) and wrapped around the body, falling underneath the right arm. The length of the thread is generally 96 times the breadth of four fingers of a man, which is believed to be equal to his height. Each of the four fingers represents one of the four states that the soul of a man experiences: waking, dreaming, dreamless sleep and knowledge of the absolute.
Yajñopavitam has three threads (actually only one thread, folded three times and tied together) each consisting of three strands. These threads represent
Goddess Gayatri (Goddess of mind),
Goddess Saraswati (Goddess of word) and
Goddess Savitri (Goddess of deed).
The knot in the middle represent the formless Brahman, the pure form of energy which pervades all. The three threads again represent the manifestation of Brahman as Srishti, Sthithi and Vinasa. The sacred thread illustrates the fact that everything in the universe emerge from and then merge with Brahman.
Ancient texts refer to the wearing of the Yajñopavitam in three forms:
One is Upavitam, where the Yajñopavitam is worn over the left shoulder and under the right arm. This is for Gods. Upavitam is also called savya
The Second is Nivitam, where the Yajñopavitam is worn around the neck and over the chest. Nivita form is to be used during Rishi Tharpana, sexual intercourse, answering the calls of nature etc. (-Shadvimsha Brahmana, Latyayana, etc.).
The third, Prachinavitam is where the Yajñopavitam is worn above the right shoulder and under the left arm. This is for Spirits and is used by men when performing the death ceremonies of an elder. Prachinavitam is also called apsavya (Katyayana Shrauta Sutra, Manusmriti, &c.).
Literally, Pravara means the most excellent (-Monier-Williams, cf. reference). Pravara is the number of the most excellent rishis who belonged to that particular gotra to which the wearer of sacred thread belongs.
Please visit the link for more details
http://en.wikipedia.org/wiki/Pravaras
The ceremony is performed when the boy is seven years old (Gharbheshu ashtame varshe).
Upanayanam should be conducted in ‘Utharayana’.
- The continuous ‘Gayathrijapam’ will make the boy educative active and intelligent.
- Traditionally, ‘Sandhya Vandanam’ should be performed three times in a day – morning, before mid-day meals and in the evening. ‘Madhyanikam’ should be performed before mid-day meals. A boy may be able to perform ‘Madhyanikam’ only on holidays now. . Sandhya Vandanam should not be neglected on the wrong notion that the boy will not find time for studies.